When a twentysomething editor gambled on her career, she created a publishing phenomenon.

An an unproven assistant editor in her early twenties, Joëlle Delbourgo got an unwelcome message: Her boss at Bantam wanted to see her. Immediately.

It was 1978, and Delbourgo was championing a new children’s title called The Cave of Time. The book was something of an anomaly: It didn’t have a plot or a main character or even a proper ending. Instead, the reader was asked to assume the role of the hero. Every few pages, he or she had to make a critical decision on how to proceed. There were about 40 possible endings, with some paths leading to glory and others ending in alien invasion, tyrannosaurus attack, and other forms of ruin. Delbourgo hoped to make it her first major acquisition.

In fact, she hoped to pursue it as a series. But as a junior voice in the company, she had no idea how her higher-ups would respond to such an experimental project. As she stepped into the cavernous office of Oscar Dystel, Bantam’s president, anxiety struck.

“I understand you’re trying to change the way kids read,” he barked. She was. And she wasn’t alone.

A decade prior, a lawyer named Edward Packard had hit upon an idea. He often told his kids bedtime stories, and whenever he couldn’t figure out how to resolve a story, he asked them to weigh in with options. He soon realized that they enjoyed the stories more when they helped choose the endings.

This interactivity was a valuable storytelling device—it both harnessed the kids’ attention and took advantage of their innate creativity—and Packard wondered whether there was a clever way to package it in book form. During his commute, he began writing a shipwreck adventure called Sugarcane Island, with multiple storylines that required reader participation.

When, in 1969, he passed his finished copy along to a friend of a friend who worked as a William Morris literary agent, the feedback was glowing. “The agent said he would be surprised if there were no takers,” Packard recalls. “Then he proceeded to be surprised.”

Island collected dust until 1975, when Vermont Crossroads Press, a publisher looking for innovative children’s books, picked it up. The press was headed by R.A. Montgomery, a former high school teacher who saw the educational value in game structure. “Experiential learning is the most powerful way for kids, or for anyone, to learn something,” Montgomery says.

Montgomery published Sugarcane Island to a nice, albeit quiet, response, and he and Packard began to write more stories. But Vermont Crossroads didn’t have great distribution. “He was not equipped to saturate the market,” Packard says. Montgomery agreed. He passed the title to a young literary agent named Amy Berkower, who tried to pitch the books to numerous houses. “The only person responsive was Joëlle,” Berkower remembers.

“I got really excited,” says Delbourgo, who also worked in Bantam’s educational division. “I said, ‘Amy, this is revolutionary.’ This is precomputer, remember. The idea of interactive fiction, choosing an ending, was fresh and novel. It tapped into something very fundamental.”

But before Delbourgo could publish the book, she had to persuade her boss at Bantam to take a risk. Dystel was skeptical at first, but Delbourgo’s presentation was convincing. She believed in the product. “He wound up becoming my biggest supporter,” she says. The “Choose Your Own Adventure” series officially launched in 1979.

Montgomery and Packard were each contracted to write six books. The first title to be picked up by Bantam was Montgomery's Journey Under the Sea, about an expedition to Atlantis. Readers were confronted with seismic choices: “If you put up the energy repulsion shields to try and escape the black hole, turn to page 22!” To stoke attention, Bantam gave away thousands of copies, flooded book fairs, and created teaching guides for classrooms. The strategy worked. By 1981, Bantam had four million copies in print.

That same year, the young daughter of New York Times culture columnist Aljean Harmetz picked up a “Choose” book and couldn’t put it down. Intrigued, Harmetz wrote a piece that described the series as being “as contagious as chicken pox.” That’s when it exploded.

To capitalize on the momentum, Bantam decided to roll out one title a month. In turning up the frequency to serial levels, the publisher hit upon another novelty that would prove irresistible. Because the books were numbered sequentially, kids started collecting them like trading cards. Years later, this savvy marketing technique would be applied to other series, including “The Baby-Sitters Club” and “Sweet Valley High.”

To keep pace with this grueling publication schedule, Packard and Montgomery—who worked separately—started subcontracting installments to other writers. (In years to come, bestselling authors like James Patterson and Tom Clancy would use this same formula, known as “packaging,” to keep up their production.) In 1981, Packard quit his law practice to write full time.

While the main “Choose” line featured a variety of adventures—Mayan exploration, deep-sea intrigue, run-ins with the abominable snowman—greater demand called for more and more spin-offs. Some, like the Star Wars and Disney tie-ins, were licensed merchandise. Others didn’t fare so well. “I tried some sports titles like 'Soccer Star' and 'Skateboard Master,' but they didn’t sell,” Packard says. Instead, he and his writers gravitated toward subjects that interested them: science, shipwrecks, African mountain gorillas.

As with most children’s trends, there was some hand-wringing over several of the more gruesome fates: Child psychologists questioned whether scary stories—say, getting sacrificed in a pagan ritual—made for reassuring bedtime reading. Packard laughed off the criticisms. “I remember getting ‘shot’ as a kid,” he says of playing cowboy. “Kids got it very quickly. You die, yes, but you take another choice and go on.”

By the late 1980s, the series was showing signs of exhaustion. Lackluster concepts like You Are a Shark were pushed through in the rush to keep the installments coming, and the number of possible endings in many titles dwindled. Early “Choose” books had dozens of endings; later entries saw as few as eight. Then, with the rise of video and computer games, which provided that same interactivity in an even more addictive format, “Choose”’s foothold in the market slipped. In 1999, after selling 250 million copies worldwide, the publisher retired the brand and let the trademark lapse.

And yet, nearly 35 years after its debut, “Choose Your Own Adventure” remains a publishing landmark. It preceded many of the long-running children’s series, like “Goosebumps,” and proved to skeptical parents that kids were still willing to crack open books. “The reading happened because kids were put in the driver’s seat. They were the mountain climber, they were the doctor, they were the deep-sea explorer,” says Montgomery. “They made choices, and so they read.”

By combining savvy marketing with an innate sense for the psychology of storytelling, Delbourgo had stumbled upon the formula for an enduring classic. At the time, the series’ success netted her a $2000 raise. (Eventually, she settled in as a literary agent.) But having a hand in birthing “Choose Your Own Adventure” held far greater rewards than Delbourgo could have anticipated. “I remember how I felt when I read the books and how excited I got, the clarity I had about them,” she says. “I couldn’t have imagined the incredible impact it had or how prescient it was.”